The effect of intramolecular H-bonds on the aqueous solution continuum description of the N-protonated form of dopamine

被引:29
作者
Alagona, G
Ghio, C
机构
[1] CNR - Ist. Chim. Quantistica E., I-56126 Pisa
关键词
D O I
10.1016/0301-0104(95)00295-2
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The conformational properties in vacuo and in solution of N-protonated dopamine have been studied making use of ab initio SCF calculations in vacuo and free energy calculations in aqueous solution, in the framework of the polarizable continuum model (PCM), on the STO-3G, 4-31G and 6-31G* optimized geometries obtained in vacuo, The in vacuo energy profiles along a few sections of the potential energy surface turn out to be very close for the extended basis sets, while the STO-3G results are slightly displaced. The largest difference between the minimal and the extended basis sets is found for the perpendicular arrangement, which is however the lowest energy profile with low barriers to the C-C-C-N rotation both in vacuo and in solution. The solvent stabilizes the trans over the gauche rotamers. The conformers without intramolecular H bonds between the -OH side chains are favored by the solvent, which makes the planar(1) anti conformers as stable as the corresponding conformers with an intramolecular H-bond in aqueous solution. The solvation free energy is considerably less basis set dependent than the potential energy in vacuo. The ab initio PCM results slightly favor the planar, form over the planar(2) form whereas the semiempirical AMSOL results of Urban, Cramer and Famini (J. Am. Chem, Sec. 114 (1992) 8226) do the opposite. The cavitation free energy is nearly independent of the basis set. The almost constant (about 4.4 kcal/mol) cavitation and dispersion-repulsion corrections do not affect the differential quantities.
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页码:239 / 249
页数:11
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